1. Field of the Invention
The present invention relates to optical assemblies, and more particularly to an optical assembly used in a Dense Wavelength Division Multiplexer (DWDM).
2. Description of the Prior Art
As optical fiber technology is being more broadly applied in the telecommunications, data communications and community antenna television (CATV) industries, the fiber optic component industry is now confronted with increasingly demanding requirements for good performance and high reliability. Currently, most design and manufacturing of in-line fiber optic components are based on optical collimators, which provide low-loss light transmission from the input fiber to the output fiber through an optical element. Optical collimators are basic building blocks of fiber optic components. The reliability and level of performance of fiber optic components depends heavily on the reliability and performance characteristics of their optical collimators.
A Graded Index (GRIN) lens is a popular optical element which is utilized in an optical collimator for collimating scattered light. As show in FIG. 1, a conventional optical collimator 18 comprises an input optical fiber 10, an output optical fiber 11, a glass ferrule 12, and a GRIN lens 13. A through hole 121 defined in the ferrule 12 receives the optical fibers 10, 11 therein. The ferrule 12 and the GRIN lens 13 are aligned and fixed in a glass inner tube 15. A stainless steel tube 16 encloses the glass inner tuber 15, thereby providing mechanical protection. A filter 14 is attached to an end face 132 of the GRIN lens 13 with the help of epoxy resin 17.
The conventional optical collimator has some disadvantages. First, the filter 14 is directly attached to a surface of the GRIN lens 13 with the epoxy resin 17. When the resin heats up during use, the filter 14 is subjected to uneven heating. This changes and adversely affects performance of the filter 14. In addition, humidity created by the epoxy resin 17 adversely affects performance of the GRIN lens 13. Second, accurate alignment between the ferrule 12 and the GRIN lens 13 depends on accurate formation of the inner tube 15. Therefore, the inner tube 15 must be made with unduly high precision. Third, the GRIN lens 13 is conventionally made by an ion exchange method, which requires that, the GRIN lens 13 must be further polished after initial formation. Furthermore, chemicals used in the ion exchange method are harmful to users and pollute the environment.
Recently, a molded collimating lens 23 as shown in FIG. 2 has been used in an optical collimator instead of a GRIN lens. The collimating lens 23 is made by a molding method. The collimating lens 23 has an aspherical forward face 232 and an oblique rearward face 231. Molded optical collimating lenses overcome the disadvantage of environmental pollution. However, a molded lens has the curved face 232, therefore fixing a filter to the curved face 232 is inconvenient. A copending application with an unknown serial number filed on Jun. 5, 2002, titled xe2x80x9cOPTICAL COLLIMATOR WITH MOLDING LENSxe2x80x9d, with the same inventors and the same assignee as the present invention, discloses one approach to this problem.
An improved optical assembly overcoming the above-described numerous disadvantages is desired.
Accordingly, an object of the present invention is to provide an inexpensive optical assembly which has good optical performance.
Another object of the present invention is to provide an optical assembly that allows easy and precise assembly of its optical components.
A further object of the present invention is to provide an optical assembly that is environmentally friendly.
To achieve the above-mentioned objects, an optical assembly in accordance with the present invention comprises an input optical fiber and an output optical fiber, a glass ferrule receiving the input and output optical fibers therein, a molded lens, and a filter. The molded lens is fixed to the ferrule, and comprises a solid cylindrical main body with an annular-shaped protrusion extending from a forward end of the main body. The main body comprises an oblique rearward end face and an aspherical forward end face opposite to the rearward end face. The ferrule has an oblique forward end face which is fixed close to and substantially parallel with the oblique rearward end face of the molded lens. The filter is attached onto an end face of the annular protrusion.
Other objects, advantages and novel features of the invention will become more apparent from the following detailed description when taken in conjunction with the accompany drawings, in which: